Pulmonary function tests and diaphragmatic compound muscle action potential in patients with sporadic amyotrophic lateral sclerosis

Sonographic Phrenic Nerve Changes in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that affects both the upper and lower motor neurons in the nervous system, causing muscle weakness and severe disability. The progressive course of the disease reduces the functional capacity of the affected patients, limits daily activities, and leads to complete dependence on caregivers, ultimately resulting in a fatal outcome. Respiratory dysfunction mostly occurs later in the disease and is associated with a worse prognosis. Forty-six participants were included in our study, with 23 patients in the ALS group and 23 individuals in the control group. The ultrasound examination of the phrenic nerve (PN) was performed by two authors using a high-resolution "Philips EPIQ 7" ultrasound machine with a linear 4-18 MHz transducer. Our study revealed that the phrenic nerve is significantly smaller on both sides in ALS patients compared to the control group (p < 0.001). Only one significant study on PN ultrasound in ALS, conducted in Japan, also showed significant results (p < 0.00001). These small studies are particularly promising, as they suggest that ultrasound findings could serve as an additional diagnostic tool for ALS.

Respiratory function tests in amyotrophic lateral sclerosis: The role of maximal voluntary ventilation

BACKGROUND

Pulmonary function tests are routinely used to measure progression in ALS. This study aimed to assess the change of various respiratory tests, in particular maximal voluntary ventilation (MVV), which evaluates respiratory endurance.

METHODS

A group of 51 patients were assessed 3 times (T1, T2, T3, separated by 5.4 months), including slow (SVC) and forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), peak expiratory flow (PEF), maximal inspiratory (MIP) and expiratory (MEP) pressures, MVV, and sniff nasal inspiratory pressure (SNIP). In addition, body mass index (BMI), ALSFRS-R and phrenic nerve responses were obtained 4 times. Patients with dementia and marked bulbar involvement were excluded.

RESULTS

Mean ALSFRS-R was high at entry (42.9) and its decline was moderately slow at 0.4/month. FVC and FEV1 declined significantly in the three time frames analysed. MVV reduced significantly only between T1-T3 and SVC between T2-T3, and MIP, MEP, PEF and SNIP did not change significantly. The amplitude and the latency of the motor response of the phrenic nerve changed significantly, and BMI declined significantly in most time periods, and ALSFRS-R changed significantly in the 4 time periods. We found a strong correlation between MVV, and FVC, SVC, FEV1, SNIP, phrenic nerve amplitude/area (p < 0.001), and markedly with PEF (rho = 0.821) and ALSFRS-R (rho = 0.713).

CONCLUSIONS

Our study of early affected patients supports the use of a set of volitional and non-volitional respiratory tests to assess disease progression, rather than any single test. We found MVV a potentially useful marker of pulmonary function in ALS.

Electrophysiological assessment of respiratory function

While the traditional lung function tests are used to assess lung capacity and pulmonary function, they cannot evaluate respiratory driving function and the integrity of the conduction pathway from the central nervous system to the respiratory motor neuron in the spinal cord and to the diaphragm. The inspiratory trigger is sent from the central nervous system through the phrenic nerve and drives the diaphragm to generate inspiratory movement. Therefore, phrenic nerve stimulation and diaphragmatic electromyography are two fundamental methods to assess respiratory function. There are several useful tools to assess respiratory motor system including electrical or magnetic phrenic nerve stimulation, diaphragmatic needle electromyography, and diaphragmatic ultrasound. By these means, physicians can assess current respiratory status in different neurological diseases that affect respiratory muscles, follow-up of the severity of respiratory impairment, help to predict the chance of successfully weaning from ventilatory support, and confirm clinical diagnoses such as diaphragmatic myoclonus. Although some of these tests require special training, applying these neurophysiological assessments in clinical practice is highly recommended.

Sleep-disordered breathing and effects of non-invasive ventilation on objective sleep and nocturnal respiration in patients with myotonic dystrophy type I

Patients with myotonic dystrophy type I (DM1) may develop nocturnal hypoventilation, requiring non-invasive ventilation. Data on long-term adherence to non-invasive ventilation, or sleep and ventilation outcomes are scarce. We retrospectively collected baseline polysomnography and capnometry results from 36 adult patients with sleep-related symptoms (42.9 ± 12.5 years, 20 female), plus follow-up sleep study records from those treated with non-invasive ventilation. Sleep-disordered breathing was found in 33 patients (91.7%) including 8 (22.2%) with daytime hypercapnia. Twenty-six patients (72.2%) showed nocturnal hypoventilation on transcutaneous capnometry. The sensitivity of oximetry to detect nocturnal hypoventilation was only 0.38. Twenty-eight patients (77.8%) showed sleep apnea, which was predominantly obstructive (n = 8), central (n = 9), or "mixed" (n = 11). Thirty-two patients were initiated on non-invasive ventilation which significantly improved ventilation and oxygenation in the first night of treatment. Follow-up revealed stable normoxia and normocapnia without deterioration of sleep outcomes for up to 52 months. Adherence to treatment was low to moderate, with substantial inter-individual variability. Sleep disordered breathing is highly prevalent in adult DM1 patients complaining of daytime sleepiness, and non-invasive ventilation significantly, rapidly and persistently improves nocturnal gas exchange. Capnometry is superior to oximetry for detection of nocturnal hypoventilation. Adherence to non-invasive ventilation remains a major issue in DM1, and long-term treatment benefits should be individually assessed.

Usefulness of phrenic latency and forced vital capacity in patients with ALS with latent respiratory dysfunction

OBJECTIVES

The pulmonary function test (PFT) is a non-invasive and easily available technique to assess respiratory function in patients with amyotrophic lateral sclerosis (ALS); however, patients with dyspnea sometimes show normal PFT findings. Herein, we investigated whether phrenic nerve conduction study (NCS) and PFT are useful to evaluate respiratory function of patients with ALS with normal value ranges in the PFT.

METHODS

We prospectively enrolled 34 patients with definite or probable ALS, who showed FVC (%) ⩾80 of predicted and 78 healthy subjects. PFT and phrenic NCS were performed with the measurement of forced vital capacity (FVC, %), forced expiratory volumes in 1s (FEV1, %), FEV1/FCV ratio (%), and phrenic compound muscle action potential amplitude, and latency.

RESULTS

Compared to healthy controls, ALS patients showed delayed phrenic nerve latency and the decrease of FVC (%) (p=0.006 and p<0.0001, respectively). ROC curve analysis demonstrated that phrenic latency (AUC=0.7655) and FVC (%) (AUC=0.8239) discriminated ALS patients from healthy subjects.

CONCLUSION

We demonstrated that ALS patients had early respiratory dysfunction, despite normal PFT findings.

SIGNIFICANCE

Phrenic latency and FVC (%) can be helpful to discriminate ALS patients with latent respiratory dysfunction from healthy subjects.

Diaphragm pacing in amyotrophic lateral sclerosis: a literature review

Amyotrophic lateral sclerosis (ALS) remains a rapidly progressive fatal degenerative disease of motor neurons for which there are few interventions to slow disease progression or improve quality of life. A diaphragm pacing system was approved by the U.S. Food and Drug Administration in September 2011 for ALS under a Humanitarian Device Exemption. News of this approval has been met with a combination of excitement and uncertainty by members of the ALS community. We review the currently available data on the diaphragm pacing system and its use in ALS. Diaphragm pacing appears to be reasonably safe in carefully selected patients, but flaws in the reporting on it thus far preclude conclusions regarding efficacy. Further study is needed.

Is there a case for diaphragm pacing for amyotrophic lateral sclerosis patients?

Respiratory pacing has advanced the long-term management of respiratory failure secondary to neurological disorders. It has an established role in curtailing invasive mechanical ventilation after upper motor neuron lesions such as spinal cord injury. There is increasing interest to expand the application of intramuscular diaphragm pacing to amyotrophic lateral sclerosis (ALS), a progressive and fatal neurodegenerative disease. Although diaphragm pacing has been offered to ALS patients, evidence-based data to determine its benefits remain lacking. The limited current literature indicates progression of respiratory dysfunction in ALS patients despite diaphragm pacing. The data from clinical trials are inadequate to substantiate its survival and sleep benefits. Its advantages over non-invasive mechanical ventilation have not been directly investigated. Furthermore, there are cautions for ALS patients to consider when opting for diaphragm pacing. Progressive degeneration of the phrenic motor neurons in classic ALS will interrupt the transmission of pacer signals to sustain diaphragm contractions. Pacing protocols that are safe for other neurological conditions may be detrimental for ALS, at least as suggested by transgenic animal models. Issues inherent to the device warrant expert intervention in implanted patients. At present, clinical effectiveness and long-term safety concerns about diaphragm pacing in ALS remain to be addressed.

Assessment of respiratory functions by spirometry and phrenic nerve studies in patients of amyotrophic lateral sclerosis

OBJECTIVE

Spirometry is the most common test recommended to monitor respiratory dysfunction in patients of amyotrophic lateral sclerosis (ALS). However, the test depends on the patient's efforts and may be difficult to conduct in patients with faciobulbar weakness. We aimed to study the role of phrenic nerve-electrophysiological studies to predict respiratory dysfunction and correlate it with the forced vital capacity (FVC) in patients of ALS.

METHODS

Forty-three unselected patients (32 male, 25 with limb-onset ALS, age 50±15 years) with clinically definite or probable ALS were included. They were evaluated at entry and after a period of 6 months with the ALS functional rating scale (ALSFRS), their respiratory subscores (ALS-FRSr), their FVC values as determined by spirometry, and phrenic nerve studies.

RESULTS

Six patients could not perform a satisfactory spirometry at the onset and during the course of illness. All the six patients had severe faciobulbar weakness. Respiratory abnormalities on spirometry were found in 85% of patients, whereas only 30% were symptomatic for respiratory dysfunction. In patients with severe respiratory dysfunction (FVC<60%), the phrenic nerve motor amplitudes (PNAMPs) were significantly reduced compared to those with mild-to-moderate respiratory dysfunction (FVC≥60%). The FVC value showed a significant correlation with the PN-AMP. Nine patients had a poor outcome (death or severe disability) at the end of a period of 6 months. Low levels of both FVC and PN-AMP were predictors of poor outcome for patients at the end of 6 months.

CONCLUSION

We conclude that respiratory dysfunction, as determined by spirometry, is common in patients of ALS. However, only about one-third of patients show symptoms of respiratory distress. Clinical symptoms of respiratory distress are unreliable predictors of respiratory failure in ALS. Measurement of PN-AMP at the time of presentation may be an additional tool to assess respiratory dysfunction in ALS. Reduced PN-AMP values may be indicative of low FVC and may have some role in the assessment of respiratory function in patients in whom a routine spirometry is not possible due to limitations arising from the illness. Both low FVC and reduced PN-AMP at the time of presentation are predictors of poor outcome for patients at the end of 6 months.